Digital image processing has undergone two significant evolutions in the 1990s. First, digital images are generally becoming higher resolution and higher quality. The consumer has access to near-photographic quality three megapixel digital cameras, for example. Scanners and printers of 600 dpi, or higher, are commonplace. Second, with the advent of the “populist” Internet and wireless technology, high speed networking now connects many types of heterogeneous display devices.
Image compression is vital as image size grows. However, because of the need to serve many different types of display devices with the same type of image, a new kind of image compression is required—image compression that is flexible at transmission and decode, not just encode. The JPEG 2000 image coding standard, ITU-T Rec.T.800/ISO/IEC 154441:2000 JPEG 2000 Image Coding System, allows one encoded image to be decoded at different resolutions, bit-rates, and with different regions without decoding any more than the minimum necessary amount of data.
The JPEG 2000 standard divides an image into tiles (rectangular regions), wavelet transform decompositions (different resolutions), codes coefficient bit-planes called layers (progressive bit-rate), components (e.g., R, G, B), and precincts (regions of wavelet coefficients). These tile-resolution-layers-component-precinct units are independently coded into JPEG 2000 packets. These packets can be identified and extracted from the codestream without decoding. This allows only the data required by a given display to be extracted and transmitted. For example, a monitor might require only 75 dpi data at a high quality while a printer might require 600 dpi data at a low quality. Both could be accommodated from one codestream.
The CREW image compression system served as a prototype for the features contained in the JPEG 2000 standard. For more information, see M. Boliek, M. J. Gormish, E. L. Schwartz, A. Keith, “Decoding compression with reversible embedded wavelets (CREW) codestreams,” Electronic Imaging, Vol. 7, No. 3, July 1998. An earlier paper on JPEG 2000 codestream “parsing” shows how to access, extract, and rearrange the data in a JPEG 2000 codestream. For more information, see G. K. Wu, M. J. Gormish, M. Boliek, “New Compression Paradigms in JPEG2000,” SPIE San Diego, July 2000. Another paper on JPEG 2000 codestream syntax shows how a codestream could be arranged for progressive transmission for a specific user interaction. For more information, see M. Boliek, J. S. Houchin, G. Wu, “JPEG 2000 Next Generation Image Compression System Features and Syntax,” Int. Conf. On Image Processing 2000, Vancouver, Canada, 12 Sep. 2000.
JPEG 2000 is a file format and compression algorithm. It does not specify the protocol or algorithms necessary to take advantage of the features in a client/server architecture, for example. The standard is similar to the Flashpix file format standardized by a consortium of companies now called the Digital Imaging Group. For more information, see Digital Imaging Group, “The Flashpix image format,” with a world wide web site at digitalimaging.org. Using the original JPEG file format, Flashpix is not as efficient as JPEG 2000. However, unlike JPEG 2000, Flashpix is paired with a protocol for interacting with images over the Internet called the Internet Imaging Protocol (IIP). For more information, see Digital Imaging Group, “The Internet Imaging Protocol.”